Whether you have your Fusion RAID storage system configured with a hot spare, perform incremental backups, or swap out large amounts of data, it's always handy to have extra drive modules around. Fusion drive modules employ hard drivs that have been selected for their superior performance, error handling, and reliability characteristics, especially when used in RAID groups. These drives are subjected to hours of additional, stringent testing to check for soft errors, vibration, and other reliability predictors. Just the sturdiest drives pass these tests and are prepared with special RAID-optimized firmware to become the building blocks of a super-reliable Fusion storage system.